U.S. patent number 4,148,940 [Application Number 05/890,562] was granted by the patent office on 1979-04-10 for method for depositing films containing cobalt oxide.
This patent grant is currently assigned to PPG Industries, Inc.. Invention is credited to J. Shannon Breininger, Charles B. Greenberg.
United States Patent |
4,148,940 |
Breininger , et al. |
April 10, 1979 |
Method for depositing films containing cobalt oxide
Abstract
Improved methods are disclosed for depositing metal oxide films
from coating compositions containing dehydrated cobaltous
acetylacetonate.
Inventors: |
Breininger; J. Shannon
(Gibsonia, PA), Greenberg; Charles B. (Murraysville,
PA) |
Assignee: |
PPG Industries, Inc.
(Pittsburgh, PA)
|
Family
ID: |
25396835 |
Appl.
No.: |
05/890,562 |
Filed: |
March 20, 1978 |
Current U.S.
Class: |
427/226;
427/255.19; 427/294; 427/314; 427/422; 428/432; 556/31; 556/40 |
Current CPC
Class: |
C03C
17/245 (20130101); C03C 17/25 (20130101); C03C
2218/152 (20130101); C03C 2218/112 (20130101); C03C
2217/217 (20130101); C03C 2217/23 (20130101) |
Current International
Class: |
C03C
17/245 (20060101); C03C 17/25 (20060101); C03C
17/23 (20060101); B05D 001/02 (); B05D
005/12 () |
Field of
Search: |
;427/226,372R,248R,248A,248B,427,165,166,168 ;260/429J,439R |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Smith; Ronald H.
Assistant Examiner: Johnson; Raymond C.
Attorney, Agent or Firm: Seidel; Donna L.
Claims
We claim:
1. In a method for depositing metal oxide coatings which comprise
cobalt oxide by thermal decomposition of a coating composition
comprising an organometallic coating reactant and an organic
solvent, the improvement which comprises:
a. dehydrating cobaltous acetylacetonate; and
b. dissolving the dehydrated cobaltous acetylacetonate in said
organic solvent.
2. The improved method according to claim 1, wherein the
organometallic coating composition is prepared by:
(a) dehydrating the cobaltous acetylacetonate; and
(b) mixing the dehydrated cobaltous acetylacetonate with an
acetylacetonate of a metal selected from the group consisting of
iron, cobalt, chromium, copper, nickel, tin, titanium, zirconium,
vanadium, and mixtures thereof.
3. The improved method according to claim 2, wherein the
dehydration of cobaltous acetylacetonate is accomplished by heating
the coating reactant in vacuo for at least about 10 hours at a
temperature of at least about 140.degree. F. (about 60.degree.
C.).
4. The improved method according to claim 2, wherein the coating
composition is dissolved in an organic solvent and is applied by
spraying onto a hot glass substrate whereupon the coating reactants
pyrolyze to form a metal oxide film.
5. The improved method according to claim 4 wherein the organic
solvent is selected from the group consisting of aliphatic
halocarbons, olefinic halocarbons, halogenated hydrocarbons and
mixtures thereof.
6. In a method for preparing an organometallic coating composition
for the deposition of coatings comprising cobalt oxide, the
improvement which comprises:
(a) dehydrating cobaltous acetylacetonate; and
(b) incorporating dehydrated cobaltous acetylacetonate into the
coating composition which further comprises an organic solvent.
7. The improved method according to claim 6, wherein the coating
composition further comprises an acetylacetonate of a metal
selected from the group consisting of iron, chromium, copper,
cobalt, nickel, tin, titanium, zirconium, vanadium and mixtures
thereof.
8. The improved method according to claim 7, wherein the coating
composition further comprises an organic solvent selected from the
group consisting of aliphatic hoalocarbons, olefinic halocarbons,
halogenated hydrocarbons and mixtures thereof.
9. A composition for the deposition of coatings comprising cobalt
oxide by thermal decomposition of an organometallic coating
composition which comprises an organic solvent, dehydrated
cobaltous acetylacetonate and an acetylacetonate of a metal
selected from the group consisting of iron, cobalt, chromium,
copper, nickel, tin, titanium, zirconium, vanadium, and mixtures
thereof.
10. The composition of claim 9 wherein the organic solvent is
selected from the group consisting of aliphatic halocarbons,
olefinic halocarbons, halogenated hydrocarbons and mixtures
thereof.
Description
BACKGROUND OF THE INVENTION
The present invention relates generally to the deposition of
coatings containing cobalt oxide either by pyrolysis of coating
reactants in solution or by chemical vapor deposition. The present
invention relates particularly to the formation of coatings
containing cobalt oxide in a mixed metal oxide spinel
structure.
In U.S. Pat. No. 3,081,200, Tompkins discloses a method for
preparing coatings containing oxides of metals, including cobalt,
by the pyrolysis of metal acetylacetones in organic solvents. In
U.S. Pat. No. 3,660,061, Donley et al disclose coating compositions
comprising organic solvents and organometallic coating reactants
including cobalt acetylacetonate. While no specific valence state
of cobalt is disclosed as preferred, commercial activity has been
developed upon the use of cobaltic acetylacetonate primarily
because common cobaltous acetylacetonate, which is hydrated, is
relatively insoluble in the organic solvents listed in U.S. Pat.
No. 3,660,061.
In U.S. Pat. No. 3,852,098, Bloss et al disclose contacting a hot
glass substrate with a gaseous mixture 50 to 100 percent saturated
with the vapors at a reactive metal compound which thermally reacts
to deposit a metal-containing coating on the surface. Based on
thermodynamic data, from the viewpoint of vaporization behavior,
cobalt III-acetylacetonates are preferred to cobalt
II-acetylacetonates for chemical vapor deposition.
It has been observed that metal oxide films formed from the
above-described coating compositions may include cobaltous oxide in
a Co.sub.3 O.sub.4 (CoO.Co.sub.2 O.sub.3) spinel structure even
though cobaltic acetylacetonate is used as the coating reactant and
the film is formed in a generally oxidizing atmosphere. This
observation leads to the belief that some proportion of cobaltic
ions are reduced to cobaltous ions prior to the deposition of
cobalt oxide.
Analysis of mixed metal oxide films formed on glass from metal
acetylacetonates either by pyrolysis of coating reactants in
solution or by chemical vapor deposition indicates that the metal
oxides tend to assume a spinel structure which is
characteristically very durable. In a spinel structure, oxygen ions
form a close packed array leaving interstitial spaces to be
occupied by the metal ions. The interstitial spaces having four
nearest neighbors are filled by cations which coordinate
tetrahedrally while the spaces having six nearest neighbors are
filled with cations which coordinate octahedrally. Some metal ions
will coordinate either tetrahedrally or octahedrally while others,
such as chromic and cobaltic, prefer octahedral coordination. In
the deposition of mixed metal oxide films, when it is desired to
form a spinel structure which has a general formula of A.sub.8
B.sub.16 O.sub.32, wherein A represents cations which are
tetrahedrally coordinated and B represents cations which are
octahedrally coordinated, it is important to have an appropriate
ratio of A and B type cations since the composition of the film may
vary depending on the relative availability of A and B type
cations.
SUMMARY OF THE PRESENT INVENTION
The present invention recognizes that cobaltic ions prefer
octahedral coordination and that in certain mixed metal coating
compositions, particularly those including organochromium
reactants, there may be competition for octahedral sites. If there
are too many octahedrally coordinating cations and too few
tetrahedrally coordinating cations, a preferred spinel structure
may be replaced by a coating of different overall structure,
composition, and durability. When it is desired to maintain a
certain ratio of metals in a cobalt-containing metal oxide coating,
but the ratio of octahedrally to tetrahedrally coordinating cations
is inappropriate for spinel formation, the present invention
provides for replacing the cobaltic ions with cobaltous ions, which
will coordinate either tetrahedrally or octahedrally, by replacing
the cobaltic acetylacetonate coating reactant with cobaltous
acetylacetonate. Although commercially available hydrated cobaltous
acetylacetonate is relatively insoluble in the commonly used
organic solvents, the present invention provides for dehydrating
the cobaltous acetylacetonate which may then be dissolved in an
organic solvent. The coating compositions of the present invention,
containing dehydrated cobaltous acetylacetonate, may be used to
deposit coatings containing cobalt oxide either by pyrolysis of a
coating solution or by solvent-free chemical vapor deposition. It
appears that the absence of water of hydration improves the
uniformity of coatings formed by chemical vapor deposition.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
A continuous ribbon of glass is formed in a bath of molten metal,
preferably tin or a tin alloy, in a refractory tank. The ribbon is
lifted from the bath at the exit end of the tank and is conveyed
through a coating area. A plurality of spray guns are positioned
above the glass ribbon to deliver a coating composition to the top
surface of the ribbon. The coating composition comprises a mixture
of metal beta diketonates, preferably metal acetylacetonates,
including dehydrated cobaltous acetylacetonate, in an organic
solvent. The dehydrated cobaltous acetylacetonate is obtained by
placing readily available hydrated cobaltous acetylacetonate in a
vacuum chamber for about 10 hours at a temperature of about
140.degree. F. (about 60.degree. C.). Shorter periods or lower
temperatures may be used with less than production quantities. The
dehydrated cobaltous acetylacetonate is readily soluble in organic
solvents such as disclosed in U.S. Pat. No. 3,660,061 which
disclosure is in whole incorporated herein by reference. The
coating composition is applied from the spray gun to the glass
surface at a rapid rate to insure uniformity of the coating. The
coating reactants pyrolyze on contact with the glass surface which
is at a temperature above about 500.degree. F. (about 260.degree.
C.), preferably from about 1000.degree. to 1200.degree. F. (about
540.degree. to 650.degree. C.) to form a mixed metal oxide film.
Preferred coating compositions comprise about 2 percent by weight
metal in an organic solvent, preferably aliphatic or olefinic
halocarbons or halogenated hydrocarbons, or mixtures thereof. The
preferred coating reactants are acetylacetonates of cobalt, iron,
nickel, chromium, copper, manganese, titanium, vanadium and
mixtures thereof. The coating compositions of the present invention
comprise dehydrated cobaltous acetylacetonate, preferably in a
mixture with ferric and chromic acetylacetonates.
The present invention will be further understood from the
descriptions of specific examples which follow.
EXAMPLE I
A mixture of acetylacetonates comprising, by weight of metal, 64
percent cobalt, 18 percent chromium and 22 percent iron is
dissolved in an organic solvent. The mixture comprises dehydrated
cobaltous acetylacetonate prepared by heating readily available
hydrated cobaltous acetylacetonate to about 140.degree. F. (about
60.degree. C.) in vacuo for about 12 hours. The total concentration
of metal in the coating solution is about 2 percent by weight. The
organic solvent is 50/50 percent by volume methylene chloride and
trichloroethylene. The coating solution is sprayed onto a surface
of a 7/32 inch (about 6 millimeters) thick clear glass substrate
which is at a temperature of about 1120.degree. F. (about
605.degree. C.). The metal acetylacetonates pyrolyze to form a
mixed metal oxide spinel-type film on the glass surface. The
luminous transmittance of the coated glass is about 38 percent.
EXAMPLE II
A mixture of acetylacetonates comprising, by weight of metal, 64
percent cobalt, 18 percent chromium and 22 percent is prepared as a
powdered solid. The mixture comprises dehydrated cobaltous
acetylacetonate as in Example I. The coating composition is
vaporized and applied to a surface of a 7/32 inch (about 6
millimeters) thick clear glass substrate by chemical vapor
deposition. A relatively texture-free mixed metal oxide spinel-type
film is formed on the glass surface. The luminous transmittance of
the coated glass is about 42 percent.
EXAMPLE III
A coating composition is prepared by dissolving dehydrated
cobaltous acetylacetonate in methylene chloride at a concentration
of 2 percent by weight cobalt. The solution is sprayed onto a glass
surface at a temperature of about 1100.degree. F. (about
593.degree. C.). The resultant cobalt oxide coated glass article
has a luminous transmittance of about 27 percent.
The above examples are offered to illustrate preferred embodiments
of the present invention. The examples relating to pyrolytic
deposition show that the use of dehydrated cobaltous
acetylacetonate is compatible with organic solvents. The examples
relating to chemical vapor deposition show that the use of
dehydrated cobaltous acetylacetonate in the chemical vapor
deposition of coatings containing cobalt oxide results in a uniform
film. Cobaltous acetylacetonate may be dehydrated under a variety
of temperature and pressure conditions requiring various periods of
time. The higher the temperature and the lower the pressure, the
shorter the period required to effectively dehydrate the cobaltous
acetylacetonate. Sufficient dehydration may be determined simply by
visual examination since the hydrated cobaltous acetylacetonate is
a fleshy pale pink colar while the dehydrated cobaltous
acetylacetonate is purple. Dehydrated cobaltous acetylacetonate may
be used alone or in combination with a variety of organometallic
coating reactants, and in a variety of solvents as well as in
powder form. Although the invention has been described in detail
with respect to cobaltous acetylacetonate, the invention also
encompasses the dehydration of hydrated nickelous and other
transition metal acetylacetonate. These hydrated acetylacetonates
have inadequate solubility in organic solvents, but upon
dehydration become sufficiently soluble to be used in coating
solutions for pyrolytic deposition of metal oxide films. The scope
of the present invention is limited only the following claims.
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